1. Field of the Invention
The present invention relates generally to marine powertrains and more specifically to systems for transmitting power from prime movers to propulsion devices, such as propellers.
2. Discussion of the Related Art
It is known that a marine vessel having a single engine that drives a single propeller can experience a propeller torque effect that forces the marine vessel to list or roll. Marine vessels having multiple engines that drive multiple propellers in the same direction of rotation can also experience listing or rolling due to propeller torque effect. Propeller torque induced listing and rolling can make controlling marine vessels difficult at times.
Accordingly, some marine vessels include a pair of engines and transmissions that rotate a pair of propellers in opposite directions. This configuration is conventionally referred to as counter-rotating propellers and it can reduce such propeller torque effects on the marine vessel. However, since most internal combustion engines are setup to operate in a single rotational direction (of their crankshafts), in order to provide a pair of counter-rotating propellers behind a pair of engines requires different configurations of the transmissions and/or final drives for each side of the marine vessel. This can lead to added expense and complexity of the design of the systems, since the components, including geometry, of the starboard side powertrain and the port side powertrain are not identical.
Furthermore, typical (i) single engine/single propeller configurations, and (ii) twin engine/twin propeller configurations, require final drive assemblies that can handle the entire torque or power output of the engine(s). Accordingly, marine vessels that utilize high torque or power outputting engines require final drive assemblies that are quite large, heavy, and expensive.
Other attempts have been made to increase propulsive efficiency and reduce propeller torque effect by providing a pair of propellers that are axially aligned, abutting each other, and driven through the same final drive assembly, but in opposite directions. This configuration is conventionally referred to as contra-rotating propellers. However, providing contra-rotating propellers typically requires a concentrically arranged pair of drive shafts, whereby the outer drive shaft must be hollow which can compromise its strength and add expense and complexity to the design.
Each of the prior systems fail to provide a solution to the problem of providing a highly efficient yet strong and compact marine drive system that uses multiple propellers in high powered marine applications.
Accordingly, there was a need for a marine power splitting gearbox that can input power from a single prime mover and distribute the power to a pair of counter-rotating propellers. A solution which minimizes complexity without compromising integrity was preferred.